{"id":"GHSA-jqff-g426-hqxp","summary":"fast-uri vulnerable to host confusion via percent-encoded scheme normalization","details":"### Impact\n\n`fast-uri` decodes percent-encoded characters in the scheme component with the legacy global `unescape()` and serializes the result back as raw characters, without re-escaping it or validating it as a scheme. A scheme that decodes to characters outside the RFC 3986 scheme grammar can therefore introduce structure the original input did not contain.\n\nFor example, `%2f%2fevil.example:/pwn` parses with no authority (`parse().host` is `undefined`), but `resolve()` and `normalize()` return `//evil.example:/pwn`, which reparses with host `evil.example`. The `%uXXXX` form (`%u002f%u002fevil.example:/pwn`) produces the same result, and a scheme containing `%0d%0a` reaches the output as a raw CR LF.\n\nApplications that normalize or resolve untrusted URLs before a redirect check, host allowlist, or outbound request decision, especially ones that treat a missing authority as same-origin, can be steered to an attacker-chosen authority, and a normalized URI placed in a response header can carry an injected CR LF.\n\n### Patches\n\nUpgrade to `fast-uri` \u003e= 4.1.3, or \u003e= 3.1.6 in the v3.x release line, or \u003e= 2.4.5 in the v2.x release line.\n\n### Workarounds\n\nNone. Upgrade to the patched version.","aliases":["CVE-2026-76172"],"modified":"2026-09-02T16:00:14.560194256Z","published":"2026-09-02T15:41:53Z","database_specific":{"github_reviewed_at":"2026-09-02T15:41:53Z","nvd_published_at":"2026-08-24T11:16:40Z","cwe_ids":["CWE-177"],"severity":"HIGH","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/fastify/fast-uri/security/advisories/GHSA-jqff-g426-hqxp"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-76172"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/37f3417c82994279656854f83ce938acd81c3862"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/a941e626411f576f8d90883231e57b6c9d0ff98b"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/c6a74bfd9d8c6b0df5362b3c7ae88d8021cb1e39"},{"type":"WEB","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"PACKAGE","url":"https://github.com/fastify/fast-uri"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v2.4.5"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v3.1.6"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v4.1.3"}],"affected":[{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.3.1"},{"fixed":"2.4.5"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-jqff-g426-hqxp/GHSA-jqff-g426-hqxp.json"}},{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"3.0.0"},{"fixed":"3.1.6"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-jqff-g426-hqxp/GHSA-jqff-g426-hqxp.json"}},{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.0.0"},{"fixed":"4.1.3"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-jqff-g426-hqxp/GHSA-jqff-g426-hqxp.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"}]}